The invention relates to systems and methods for cleaning and/or processing parts. In particular, the invention relates to ultrasound systems, ultrasound generators, ultrasound transducers, and methods which support or enhance the application of ultrasound energy within liquid.
The present invention relates to ultrasound cleaning systems, and more particularly, to systems, generators, transducers, circuitry and methods that clean and/or process by coupling sound waves into a liquid. Prior art ultrasound systems lack the ability to remove a wide range of particle types and sizes without doing damage to the part being cleaned or processed. This invention improves the performance of an ultrasound system while eliminating the damage causing mechanisms.
As defined in the technical literature, xe2x80x9cultrasoundxe2x80x9d, xe2x80x9cultrasonicxe2x80x9d and xe2x80x9cultrasonicsxe2x80x9d generally refer to acoustic disturbances in a frequency range above about eighteen kilohertz (khz) and which extend upwards to over four megahertz (Mhz). As is commonly used in the cleaning industry and as used herein, xe2x80x9cultrasonicxe2x80x9d will generally refer to acoustic disturbances in a frequency range above about eighteen kilohertz and extending up to about 90 khz. Ultrasound and ultrasonics will be used to mean the complete range of acoustic disturbances from about 18 khz to 4 Mhz, except when they are use with terms such as xe2x80x9clower frequencyxe2x80x9d ultrasound, xe2x80x9clow frequencyxe2x80x9d ultrasound, xe2x80x9clower frequencyxe2x80x9d ultrasonics, or xe2x80x9clow frequencyxe2x80x9d ultrasonics, then they will mean ultrasound between about 18 khz and 90 khz. xe2x80x9cMegasonicsxe2x80x9d or xe2x80x9cmegasonicxe2x80x9d refer to acoustic disturbances between about 600 khz and 4 Mhz. The prior art has manufactured xe2x80x9clow frequencyxe2x80x9d and xe2x80x9cmegasonicxe2x80x9d ultrasound systems. Typical prior art low frequency systems, for example, operate at 25 khz, 40 khz, and as high as 90 khz. Typical prior art megasonic systems operate between 600 khz and 1 Mhz. Certain aspects of the invention apply to low frequency ultrasound and to megasonics. However, certain aspects of the invention apply to ultrasound in the 100 khz to 350 khz region, a frequency range which is sometimes denoted herein as xe2x80x9cmicrosonicxe2x80x9d or xe2x80x9cmicrosonics.xe2x80x9d The upper end of the microsonic frequency range from about 300 khz to 350 khz is called herein xe2x80x9chigher microsonicsxe2x80x9d or xe2x80x9chigher frequency microsonicxe2x80x9d.
As used herein, xe2x80x9cresonant transducerxe2x80x9d means a transducer operated at a frequency or in a range of frequencies that correspond to a one-half wavelength (xcex) of sound in the transducer stack. xe2x80x9cHarmonic transducerxe2x80x9d means a transducer operated at a frequency or in a range of frequencies that correspond to 1xcex, 1.5xcex, 2xcex or 2.5xcex of sound, and so on, in the transducer stack. The harmonics of a practical physical structure are often not exact integer multiples of the fundamental frequency, the literature sometimes refer to these non-integer harmonics as overtones. Herein, harmonics will mean resonances higher in frequency than the fundamental resonant frequency. xe2x80x9cBandwidthxe2x80x9d means the range of frequencies in a resonant or harmonic region of a transducer over which the acoustic power output of a transducer remains between 50% and 100% of the maximum value.
As used herein, a xe2x80x9cdelicate partxe2x80x9d refers to those parts which are undergoing a manufacture, process, or cleaning operation within liquid subjected to ultrasound energy. By way of example, one delicate part is a semiconductor wafer which has extremely small features and which is easily damaged by cavitation implosion. Another delicate part is a modern jet engine turbine blade which can fracture if excited into resonant vibration. A delicate part often defines components in the computer industry, including disk drives, semiconductor components, and the like.
As used herein, xe2x80x9ckhzxe2x80x9d refers to kilohertz and a frequency magnitude of one thousand hertz. xe2x80x9cMhzxe2x80x9d refers to megahertz and a frequency magnitude of one million hertz.
As used herein, xe2x80x9csuccessive frequenciesxe2x80x9d are two or more waveforms that are produced, one at a time, in a series fashion, where at least two different frequencies exist within the set of waveforms. At the output of a generator, these waveforms generally form an AC voltage. In an ultrasound tank, these waveforms are normally represented by an ultrasound wave in the liquid.
As used herein, successive frequencies are said to xe2x80x9csweepxe2x80x9d when the period or the half period of two or more of the waveforms are unequal to each other.
Sweeping frequency generators change their output frequency through successive frequencies in a bandwidth, e.g., sweeping from the lowest frequency in a chosen bandwidth through the bandwidth to the highest frequency in the chosen bandwidth, then sweeping from this highest frequency through the bandwidth back to the lowest frequency. The function of time for these frequency changes is typically linear, but other functions of time, such as part of an exponential, are possible. As used herein, xe2x80x9csweep frequencyxe2x80x9d refers to the reciprocal of the time that it takes for successive frequencies to make a round trip, for example, change from one frequency through the other frequencies and back to the original frequency. Although sweep rate might technically be interpreted as the rate of change from one successive frequency to the next, the more common usage for sweep rate will be used herein; that is, xe2x80x9csweep ratexe2x80x9d means the same as sweep frequency. It is generally undesirable to operate an ultrasound transducer at a fixed, single frequency because of the resonances created at that frequency. Therefore, an ultrasound generator can sweep the operational frequency through some or all of the available frequencies within the transducer""s bandwidth at a xe2x80x9csweep rate.xe2x80x9d Accordingly, particular frequencies have only short duration during the sweep cycle (i.e., the time period for sweeping the ultrasound frequency up and down through a range of frequencies within the bandwidth). xe2x80x9cSweep the sweep ratexe2x80x9d or xe2x80x9cdouble sweepingxe2x80x9d or xe2x80x9cdual sweepxe2x80x9d refer to an operation of changing the sweep rate as a function of time. In accord with the invention, xe2x80x9csweeping the sweep ratexe2x80x9d generally refers to the operation of sweeping the sweep rate so as to reduce or eliminate resonances generated at a single sweep frequency. xe2x80x9cRandom sweep ratexe2x80x9d or xe2x80x9cchaotic sweep ratexe2x80x9d refer to sweep rates where the successive sweep rates are numbers that are described by no well defined function, i.e., random or chaotic numbers.
The present invention concerns the applied uses of ultrasound energy, and in particular the application and control of ultrasonics to clean and process parts within a liquid. Generally, in accord with the invention, one or more ultrasound generators drive one or more ultrasound transducers, or arrays of transducers, coupled to a liquid to clean and/or process the part. The liquid is preferably held within a tank; and the transducers mount on or within the tank to impart ultrasound into the liquid. In this context, the invention is particularly directed to one or more of the following aspects and advantages:
(1) By utilizing harmonics of certain clamped ultrasound transducers, the invention generates, in one aspect, ultrasound within the liquid in a frequency range of between about 100 khz to 350 khz (i.e., xe2x80x9cmicrosonicxe2x80x9d frequencies). This has certain advantages over the prior art. In particular, unlike prior art ultrasonic systems which operate at less than 100 khz, the invention eliminates or greatly reduces damaging cavitation implosions within the liquid. Further, the transducers operating in this frequency range provide relatively uniform microstreaming, such as provided by megasonics; but they are also relatively rugged and reliable, unlike megasonic transducer elements. In addition, and unlike megasonics, microsonic waves are not highly collimated, or xe2x80x9cbeam-like,xe2x80x9d within liquid; and therefore efficiently couple into the geometry of the ultrasound tank. Preferably, the application of microsonic frequencies to liquid occurs simultaneously with a sweeping of the microsonic frequency within the transducer""s harmonic bandwidth. That is, microsonic transducers (clamped harmonic transducers) are most practical when there is a sweep rate of the applied microsonic frequency. This combination reduces or eliminates (a) standing waves within the liquid, (b) other resonances, (c) high energy cavitation implosions, and (d) non-uniform sound fields, each of which is undesirable for cleaning or processing semiconductor wafers and delicate parts.
(2) The ultrasound transducers or arrays of the invention typically have a finite bandwidth associated with the range of frequencies about a resonant or harmonic frequency. When driven at frequencies within the bandwidth, the transducers generate acoustic energy that is coupled into the liquid. In one aspect, the invention drives the transducers such that the frequency of applied energy has a sweep rate within the bandwidth; and that sweep rate is also varied so that the sweep rate is substantially non-constant during operation. For example, the sweep rate can change linearly, randomly, chaotically or as some other function of time. In this manner, the invention reduces or eliminates resonances which are created by transducers operating with a single sweep rate, such as provided in the prior art.
(3) At least one ultrasound generator of the invention utilizes amplitude modulation (AM). However, unlike the prior art, this AM generator operates by selectively changing the AM frequency over time. In a preferred aspect of the invention, the AM frequency is swept through a range of frequencies which reduce or eliminate low frequency resonances within the liquid and the part being processed. Accordingly, the AM frequency is swept through a range of frequencies; and this range is typically defined as about 10-40% of the optimum AM frequency. The optimum AM frequency is usually between about 1 hz and 10 khz. Therefore, for example, if the optimum AM frequency is 1 khz, then the AM frequency is swept through a frequency range of between about 850 hz and 1150 hz. In addition, the rate at which these frequencies are varied is usually less than about {fraction (1/10)}th of the optimum AM frequency. In this example, therefore, the AM sweep rate is about 100 hz. These operations of sweeping the AM frequency through a range of frequencies and at a defined AM sweep rate reduce or eliminate unwanted resonances which might otherwise occur at the optimum AM frequency. In another aspect of the invention, for delicate parts with very low frequency resonances, the AM frequency is changed randomly or chaotically or the AM sweep rate is swept at a function of time with a frequency about {fraction (1/10)}th of the AM sweep rate. This random or chaotic AM frequency in combination with the random or chaotic sweep rate of (3) provides elimination of low frequencies in a cleaning liquid, therefore, eliminating low frequency resonances. This combination is sometimes referred to as CRAM.
(4) The invention provides AM control by selecting a portion of the rectified power line frequency (e.g., 60 hz in the United States and 50 hz in Europe). In one aspect, this AM control is implemented by selecting a portion of the leading quarter sinusoid in a full wave amplitude modulation pattern that ends at the required amplitude in the zero to 90xc2x0 and the 180xc2x0 to 270xc2x0 regions. Another AM control is implemented by selecting a portion of the leading quarter sinusoid in a half wave amplitude modulation pattern that ends at the required amplitude in the zero to 90xc2x0 region.
(5) The invention can utilize several tanks, transducers and generators simultaneously to provide a wet bath of different chemistries for the delicate part. In one aspect, when two or more generators are operating at the same time, the invention synchronizes their operation to a common FM signal so that each generator can be adjusted; through AM, to control the process characteristics within the associated tank. In this manner, undesirable beating effects or cross coupling between multiple tanks are reduced or eliminated. In a preferred aspect, a master generator provides a common FM signal to the other generators, each operating as a slave generator coupled to the master generator, and each slave generator provides AM selectively. In addition, because the transducers in the several tanks are sometimes swept through the frequencies of the transducer""s bandwidth, the FM control maintains overall synchronization even though varying AM is applied to the several transducers. The multi-generator FM synchronization also applies to single tank ultrasound systems. That is, the invention supports the synchronized operation of a plurality of generators that are connected to a single tank. In this case, each generator has an associated harmonic transducer array and is driven with a common FM signal and AM signal so that the frequencies within the tank are synchronized, in magnitude and phase, to reduce or eliminate unwanted resonances which might otherwise occur through beating effects between the multiple generators and transducers.
(6) In another aspect, the invention utilizes two or more transducers, in combination, to broaden the overall bandwidth of acoustical energy applied to the liquid around the primary frequency or one of the harmonics. For example, the invention of one aspect has two clamped transducers operating at their first, second third, or fourth harmonic frequency between about 100 khz and 350 khz. The center harmonic frequency of each is adjusted so as to be different from each other. However, their bandwidths are made to overlap such that an attached generator can drive the transducers, in combination, to deliver ultrasound to the liquid in a broader bandwidth. In a preferred aspect, two or more transducers, or transducer arrays, operate at unique harmonic frequencies and have finite bandwidths that overlap with each of the other transducers. If, for example, each transducer has a bandwidth of 4 khz, then two such transducers can approximately provide a 8 khz bandwidth, and three such transducers can approximately provide a 12 khz bandwidth, and so on.
(7) In one aspect, the invention provides a single tank system which selects a desired frequency, or range of frequencies, from a plurality of connected ultrasound generators. Specifically, two or more generators, each operating or optimized to generate a range of frequencies, are connected to a mux; and the system selects the desired frequency range, and hence the right generator, according to the cavitation implosion energy that is desired within the tank chemistry.
(8) The invention has additional and sometimes greater advantages in systems and methods which combine one or more of the features in the above paragraphs (1) through (7). By way of example, one particularly useful system combines two or more microsonic transducers (i.e., paragraph 1) to create broadband microsonics (i.e., paragraph 6) within liquid. Such a system can further be controlled to provide a specific amplitude modulation (i.e., paragraph 4). Examples of other systems and methods of the invention are realized with the following combinations: (2) and (4); (1), (2) and (4); and (1) and (2) with frequency sweeping of the microsonic frequency.
The following patents, each incorporated herein by reference, provide useful background to the invention in the area of ultrasound generators: U.S. Pat. Nos. 3,152,295; 3,293,456; 3,629,726; 3,638,087; 3,648,188; 3,651,352; 3,727,112; 3,842,340; 4,044,297; 4,054,848; 4,069,444; 4,081,706; 4,109,174; 4,141,608; 4,156,157; 4,175,242; 4,275,363; and 4,418,297. Further, U.S. Pat. Nos. 4,743,789 and 4,736,130 provide particularly useful background in connection with ultrasound generators that are suitable for use with certain aspects of the invention, and are, accordingly incorporated herein by reference.
Clamped ultrasound transducers suitable for use with the invention are known in the art. For example, the following patents, each incorporated herein by reference, provide useful background to the invention: U.S. Pat. Nos. 3,066,232; 3,094,314; 3,113,761; 3,187,207; 3,230,403; 3,778,758; 3,804,329 and RE No. 25,433.
Techniques for mounting or affixing transducers within the tank, and of arranging the transducer and/or tank geometry are, for example, described in U.S. Pat. Nos. 4,118,649; 4,527,901; 4,543,130; and 4,836,684. Each of these patents is also incorporated by reference.
Single chamber ultrasound processing systems are described, for example, in U.S. Pat. Nos. 3,690,333; 4,409,999; 5,143,103; and 5,201,958. Such systems provide additional background to the invention and are, accordingly, incorporated herein by reference.
In one aspect, the invention provides a system for delivering broadband ultrasound to liquid. The system includes first and second ultrasound transducers. The first transducer has a first frequency and a first ultrasound bandwidth, and the second transducer has a second frequency and a second ultrasound bandwidth. The first and second bandwidths are overlapping with each other and the first frequency is different from the second frequency. An ultrasound generator drives the transducers at frequencies within the bandwidths. Together, the first and second transducers and the generator produce ultrasound within the liquid and with a combined bandwidth that is greater than either of the first and second bandwidths.
In another aspect, the system of the invention includes a third ultrasound transducer that has a third frequency and a third ultrasound bandwidth. The third bandwidth is overlapping with at least one of the other bandwidths, and the third frequency is different from the first and second frequencies. The generator in this aspect drives the third transducer within the third bandwidth so as to produce ultrasound within the liquid and with a combined bandwidth that is greater than either of the first, second and third bandwidths.
Preferably, each of the transducers are clamped so as to resist material strain and fatigue. In another aspect, each of the first and second frequencies are harmonic frequencies of the transducer""s base resonant frequency. In one aspect, these harmonic frequencies are between about 100 khz and 350 khz.
In another aspect, the system includes at least one other synergistic ultrasound transducer that has a synergistic frequency and a synergistic ultrasound bandwidth. As above, the synergistic bandwidth is overlapping with at least one of the other bandwidths, and the synergistic frequency is different from the first and second frequencies. The generator drives the synergistic transducer within the synergistic bandwidth so as to produce ultrasound within the liquid and with a combined bandwidth that is greater than any of the other bandwidths. In one aspect, this synergistic frequency is a harmonic frequency between about 100 khz and 350 khz.
In other aspects, the bandwidths of combined transducers overlap so that, in combination, the transducers produce ultrasound energy at substantially all frequencies within the combined bandwidth. Preferably, the combined operation provides ultrasound with relatively equal power for any frequency in the combined bandwidth. Using the full width half maximum (FWHM) to define each bandwidth, the bandwidths preferably overlap such that the power at each frequency within the combined bandwidth is within a factor of two of ultrasound energy produced at any other frequency within the combined bandwidth.
In another aspect, a system is provided for delivering ultrasound to liquid. The system has an ultrasound transducer with a harmonic frequency between about 100 khz and 350 khz and within an ultrasound bandwidth. A clamp applies compression to the transducer. An ultrasound generator drives the transducer at a range of frequencies within the bandwidth so as to produce ultrasound within the liquid.
In still another aspect, the system can include at least one other ultrasound transducer that has a second harmonic frequency within a second bandwidth. As above, the second frequency is between about 100 khz and 350 khz, and the second bandwidth is overlapping, in frequency, with the ultrasound bandwidth. The generator drives the transducers at frequencies within the bandwidths so as to produce ultrasound within the liquid and with a combined bandwidth that is greater than the bandwidth of a single transducer.
Another aspect of the invention provides a system for delivering ultrasound to liquid. In such a system, one or more ultrasound transducers have an operating frequency within an ultrasound bandwidth. An ultrasound generator drives the transducers at frequencies within the bandwidth, and also changes the sweep rate of the frequency continuously so as to produce non-resonating ultrasound within the liquid.
Preferably, the generator of the invention changes the sweep rate frequency in one of several ways. In one aspect, for example, the sweep rate is varied as a function of time. In another aspect, the sweep rate is changed randomly or chaotically. Typically, the sweep rate frequency is changed through a range of frequencies that are between about 10-50% of the optimum sweep rate frequency. The optimum sweep rate frequency is usually between about 1 hz and 1.2 khz; and, therefore, the range of frequencies through which the sweep rate is varied can change dramatically. By way of example, if the optimum sweep rate is 500 hz, then the range of sweep rate frequencies is between about 400 hz and 600 hz; and the invention operates by varying the sweep rate within this range linearly, randomly or chaotically, or as a function of time, so as to optimize processing characteristics within the liquid.
The invention further provides a system for delivering ultrasound to liquid. This system includes one or more ultrasound transducers, each having an operating frequency within an ultrasound bandwidth. An amplitude modulated ultrasound generator drives the transducers at frequencies within the bandwidth. A generator subsystem also changes the modulation frequency of the AM, continually, so as to produce ultrasound within the liquid to prevent low frequency resonances at the AM frequency.
Preferably, the subsystem sweeps the AM frequency at a sweep rate between about 1 hz and 100 hz. For extremely sensitive parts and/or tank chemistries, the invention can further sweep the AM sweep rate as a function of time so as to eliminate possible resonances which might be generated by the AM sweep rate frequency. This sweeping of the AM sweep rate occurs for a range of AM sweep frequencies generally defined by 10-40% of the optimum AM sweep rate. For example, if the optimum AM sweep rate is 150 hz, then one aspect of the invention changes the AM sweep rate through a range of about 130 hz and 170 hz.
In one aspect, the invention also provides amplitude control through the power lines. Specifically, amplitude modulation is achieved by selecting a portion of a leading quarter sinusoid, in a full wave amplitude modulation pattern, that ends at a selected amplitude in a region between zero and 90xc2x0 and between 180xc2x0 and 270xc2x0 of the sinusoid. Alternatively, amplitude control is achieved by selecting a portion of a leading quarter sinusoid, in a half wave amplitude modulation pattern, that ends at a selected amplitude between zero and 90xc2x0 of the sinusoid.
In still another aspect, a system of the invention can include two or more ultrasound generators that are synchronized in magnitude and phase so that there is substantially zero frequency difference between signals generated by the generators. Preferably, a timing signal is generated between the generators to synchronize the signals. In one aspect, a FM generator provides a master frequency modulated signal to each generator to synchronize the signals from the generators.
A generator of the invention can also be frequency modulated over a range of frequencies within the bandwidth of each transducer. In another aspect, the frequency modulation occurs over a range of frequencies within the bandwidth of each transducer, and the generator is amplitude modulated over a range of frequencies within the bandwidth of each transducer.
The systems of the invention generally include a chamber for holding the solution or liquid which is used to clean or process objects therein. The chamber can include, for example, material such as 316L stainless steel, 304 stainless steel, polytetrafluoroethylene, fluorinated ethylene propylene, polyvinylidine fluoride, perfluoro-alkoxy, polypropylene, polyetheretherketone, tantalum, Teflon coated stainless steel, titanium, hastalloy, and mixtures thereof.
It is preferable that the transducers of the system include an array of ultrasound transducer elements.
The invention also provides a method of delivering broadband ultrasound to liquid, including the steps of: driving a first ultrasound transducer with a generator at a first frequency and within a first ultrasound bandwidth, and driving a second ultrasound transducer with the generator at a second frequency within a second ultrasound bandwidth that overlaps at least part of the first bandwidth, such that the first and second transducers, in combination with the generator, produce ultrasound within the liquid and with a combined bandwidth that is greater than any of the first and second bandwidths.
In other aspects, the method includes the step of compressing at least one of the transducers, and/or the step of driving the first and second transducers at harmonic frequencies between about 100 khz and 350 khz.
Preferably, the method includes the step of arranging the bandwidths to overlap so that the transducers and generator produce ultrasound energy, at each frequency, that is within a factor of two of ultrasound energy produced by the transducers and generator at any other frequency within the combined bandwidth.
The application of broadband ultrasound has certain advantages. First, it increases the useful bandwidth of multiple transducer assemblies so that the advantages to sweeping ultrasound are enhanced. The broadband ultrasound also gives more ultrasound intensity for a given power level because there are additional and different frequencies spaced further apart in the ultrasound bath at any one time. Therefore, there is less sound energy cancellation because only frequencies of the same wavelength, the same amplitude and opposite phase cancel effectively.
In one aspect, the method of the invention includes the step of driving an ultrasound transducer in a first bandwidth of harmonic frequencies centered about a microsonic frequency in the range of 100 khz and 350 khz. For protection, the transducer is preferably compressed to protect its integrity.
Another method of the invention provides the following steps: coupling one or more ultrasound transducers to the liquid, driving, with a generator, the transducers to an operating frequency within an ultrasound bandwidth, the transducers and generator generating ultrasound within the liquid, changing the frequency within the bandwidth at a sweep rate, and continuously varying the sweep rate as a function of time so as to reduce low frequency resonances.
In other aspects, the sweep rate is varied according to one of the following steps: sweeping the sweep rate as a function of time; linearly sweeping the sweep rate as a function of time; and randomly or chaotically sweeping the sweep rate. Usually, the optimum sweep frequency is between about 1 hz and 1.2 khz, and therefore, in other aspects, the methods of the invention change the sweep rate within a range of sweep frequencies centered about an optimum sweep frequency. Typically, this range is defined by about 10-50% of the optimum sweep frequency. For example, if the optimum sweep frequency is 800 hz, then the range of sweep frequencies is between about 720 hz and 880 hz. Further, and in another aspect, the rate at which the invention sweeps the sweep rate within this range is varied at less than about {fraction (1/10)}th of the optimum frequency. Therefore, in this example, the invention changes the sweep rate at a rate that is less than about 80 hz.
Another method of the invention provides for the steps of (a) generating a drive signal for one or more ultrasound transducers, each having an operating frequency within an ultrasound bandwidth, (b) amplitude modulating the drive signal at a modulation frequency, and (c) sweeping the modulation frequency, selectively, as to produce ultrasound within the liquid.
The invention is particularly useful as an ultrasound system which couples acoustic energy into a liquid for purposes of cleaning parts, developing photosensitive polymers, and stripping material from surfaces. The invention can provide many sound frequencies to the liquid by sweeping the sound through the bandwidth of the transducers. This provides at least three advantages: the standing waves causing cavitation hot spots in the liquid are reduced or eliminated; part resonances within the liquid at ultrasound frequencies are reduced or eliminated; and the ultrasound activity in the liquid builds up to a higher intensity because there is less cancellation of sound waves.
In one aspect, the invention provides an ultrasound bath with transducers having at least two different resonant frequencies. In one configuration, the resonant frequencies are made so that the bandwidths of the transducers overlap and so that the impedance versus frequency curve for the paralleled transducers exhibit maximum flatness in the resonant region. For example, when a 40 khz transducer with a 4.1 khz bandwidth is put in parallelxe2x80x94i.e., with overlapping bandwidthsxe2x80x94with a 44 khz transducer with a 4.2 khz bandwidth, the resultant bandwidth of the multiple transducer assembly is about 8 khz. If transducers with three different frequencies are used, the bandwidth is approximately three times the bandwidth of a single transducer.
In another aspect, a clamped transducer array is provided with a resonant frequency of 40 khz and a bandwidth of 4 khz. The array has a second harmonic resonant frequency at 104 khz with a 4 khz harmonic bandwidth. Preferably, the bandwidth of this second harmonic frequency resonance is increased by the methods described above for the fundamental frequency of a clamped transducer array.
In one aspect, the invention provides a method and associated circuitry which constantly changes the sweep rate of an ultrasound transducer within a range of values that is in an optimum process range. For example, one exemplary process can have an optimum sweep rate in the range 380 hz to 530 hz. In accord with one aspect of the invention, this sweep rate constantly changes within the 380 hz to 530 hz range so that the sweep rate does not set up resonances within the tank and set up a resonance at that rate.
The invention provides for several methods to change the sweep rate. One of the most effective methods is to generate a random or chaotic change in sweep rate within the specified range. A simpler method is to sweep the sweep rate at some given function of time, e.g., linearly. One problem with sweeping the sweep rate is that the sweeping function of time has a specific frequency which may itself cause a resonance. Accordingly, one aspect of the invention is to sweep this time function; however, in practice, the time function has a specific frequency lower than the lowest resonant frequency of the semiconductor wafer or delicate part, so there is little need to eliminate that specific frequency.
Most prior art ultrasound systems are amplitude modulated at a low frequency, typically 50 hz, 60 hz, 100 hz, or 120 hz. One ultrasound generator, the proSONIK(trademark) sold by Ney Ultrasonics Inc., and produced according to U.S. Pat. No. 4,736,130, permits the generation of a specific amplitude modulation pattern that is typically between 50 hz to 5 khz. However, the specific amplitude modulation frequency can itself be a cause of low frequency resonance in an ultrasound bath if the selected amplitude modulation frequency is a resonant frequency of the delicate part.
Accordingly, one aspect of the invention solves the problem of delicate part resonance at the amplitude modulation frequency by randomly or chaotically changing or sweeping the frequency of the amplitude modulation within a bandwidth of amplitude modulation frequencies that satisfy the process specifications. For cases where substantially all of the low frequencies must be eliminated, random or chaotic changes of the modulation frequency are preferred. For cases where there are no resonances in a part below a specified frequency, the amplitude modulation frequency can be swept at a frequency below the specified frequency.
Random or chaotic changing or sweeping of the amplitude modulation frequency inhibits low frequency resonances because there is little repetitive energy at a frequency within the resonant range of the delicate part or semiconductor wafer. Accordingly, a resonant condition does not build up, in accord with the invention, providing obvious advantages.
The invention also provides relatively inexpensive amplitude control as compared to the prior art. One aspect of the invention provides amplitude control with a full wave or half wave amplitude modulated ultrasound signal. For full wave, a section of the 0xc2x0 to 90xc2x0 and the 180xc2x0 to 270xc2x0 quarter sinusoid is chosen which ends at the required (desired) amplitude. For example, at the zero crossover of the half sinusoid (0xc2x0 and 180xc2x0), a monostable multivibrator is triggered. It is set to time out before 90xc2x0 duration, and specifically at the required amplitude value. This timed monostable multivibrator pulse is used to select that section of the quarter sinusoid that never exceeds the required amplitude.
In one aspect, the invention also provides an adjustable ultrasound generator. One aspect of this generator is that the sweep rate frequency and the amplitude modulation pattern frequency are randomly or chaotically changed or swept within the optimum range for a selected process. Another aspect is that the generator drives an expanded bandwidth clamped piezoelectric transducer array at a harmonic frequency from 100 khz to 350 khz.
Such a generator provides several improvements in the problematic areas affecting lower frequency ultrasonics and megasonics: uncontrolled cavitation implosion, unwanted resonances, unreliable transducers, and standing waves. Instead, the system of the invention provides uniform microstreaming that is critical to semiconductor wafer and other delicate part processing and cleaning.
In another aspect of the invention, an array of transducers is used to transmit sound into a liquid at its fundamental frequency, e.g., 40 khz, and at each harmonic frequency, e.g., 72 khz or 104 khz. The outputs of generators which have the transducer resonant frequencies and harmonic frequencies are connected through relays to the transducer array. One generator with the output frequency that most closely producers the optimum energy in each cavitation implosion for the current process chemistry is switched to the transducer array.
In yet another aspect, the invention reduces or eliminates low frequency beat resonances created by multiple generators by synchronizing the sweep rates (both in magnitude and in phase) so that there is zero frequency difference between the signals coming out of multiple generators. In one aspect, the synchronization of sweep rate magnitude and phase is accomplished by sending a timing signal from one generator to each of the other generators. In another aspect, a master FM signal is generated that is sent to each xe2x80x9cslavexe2x80x9d power module, which amplifies the master FM signal for delivery to the transducers. At times, the master and slave aspect of the invention also provides advantages in eliminating or reducing the beat frequency created by multiple generators driving a single tank.
However, when multiple generators are driving different tanks in the same system, this master and slave aspect may not be acceptable because the AM of the FM signal is usually different for different processes in the different tanks. Accordingly, and in another aspect, a master control is provided which solves this problem. The master control of the invention has a single FM function generator (sweeping frequency signal) and multiple AM function generators, one for each tank. Thus, every tank in the system receives the same magnitude and phase of sweep rate, but a different AM as set on the control for each generator.
The invention also provides other advantages as compared to the prior art""s methods for frequency sweeping ultrasound within the transducer""s bandwidth. Specifically, the invention provides a sweeping of the sweep rate, within the transducer""s bandwidth, such that low frequency resonances are reduced or eliminated. Prior art frequency sweep systems had a fixed sweep frequency that is selectable, once, for a given application. One problem with such prior art systems is that the single low frequency can set up a resonance in a delicate part, for example, a read-write head for a hard disk drive.
The invention also provides advantages in that the sweep frequency of the sweep rate can be adjusted to conditions within the tank, or to the configuration of the tank or transducer, or even to a process chemistry.
The invention also has certain advantages over prior art single chamber ultrasound systems. Specifically, the methods of the invention, in certain aspects, use different frequency ultrasonics for each different chemistry so that the same optimum energy in each cavitation implosion is maintained in each process or cleaning chemistry. According to other aspects of the invention, this process is enhanced by selecting the proper ultrasound generator frequency that is supplied at the fundamental or harmonic frequency of the transducers bonded to the single ultrasound chamber.
In another aspect, the invention provides ultrasound transducer apparatus. In the apparatus, at least one ceramic drive element is sandwiched between a front driver and a backplate. The drive element has electrical contacts or electrodes mounted on either face and is responsive to voltages applied to the contacts or electrodes so as to produce ultrasound energy. A connecting elementxe2x80x94e.g., a boltxe2x80x94connects the back plate to the front driver and compresses the drive element therebetween. In accord with the invention, the front driver and/or the backplate are shaped so that the apparatus produces substantially uniform power as a function of frequency over a range of frequencies. In another aspect, the shape of the driver and/or backplate are selected so as to provide a varying power function as a function of frequency.
In another aspect, a multi-frequency ultrasound generator is provided. In one aspect, the generator includes a constant power output circuit with means for switching the center frequency of the output signal selectively. The switching means operates such that little or no intermediate frequencies are output during transition between one center frequency and another.
Another multi-frequency generator of the invention includes two or more circuits which independently create ultrasound frequencies. By way of example, one circuit can generate 40 khz ultrasound energy; while another circuit can generate 104 khz energy. A switching network connects the plurality of circuits such that the generator is shut down and relay switching takes place in a zero voltage condition. As above, therefore, the switching occurs such that little or no intermediate frequencies are output during transition between one center frequency and another.
In still another aspect, a two stage ultrasound processing system is provided. The system includes (a) one or more transducers with a defined ultrasound bandwidth defined by an upper frequency and a lower frequency. The system further includes (b) a frequency generator for driving the transducers from the upper frequency to the lower frequency over a selected or variable time period and (c) a process tank connected with the transducers so as to generate ultrasound energy within the tank at frequencies defined by the generator. During a given cycle, the generator drives the transducers from the upper frequency to the lower frequency. Once the lower frequency is reached, a frequency control subsystem controls the generator so as to drive the transducers again from upper to lower frequency and without driving the transducers from lower to upper frequencies. In this manner, only decreasing frequenciesxe2x80x94per cyclexe2x80x94are imparted to process chemistries. The system thus provides for removing contamination as the downward cycling frequencies cause the acoustic energy to migrate in an upwards motion inside the tank which in turn pushes contamination upwards and out of the tank.
In another aspect of the invention, the two stage ultrasound processing system includes means for cycling from upper-to-lower frequencies every half cycle. That is, once the transducers are driven from upper to lower frequencies over a first half cycle, the generator recycles such that the next half cycle again drives the transducers from upper to lower frequencies. Alternatively, after driving the transducers from upper to lower frequencies for a first half cycle, the system inhibits the flow of energy into the tank over a second half cycle.
The two stage ultrasound processing systems of the invention can be continuous or intermittent. That is, in one preferred aspect, the system cycles from upper to lower frequencies and then from lower to upper frequencies in a normal mode; and then only cycles from upper to lower frequencies in a contamination removing mode.
In still another aspect, the invention provides a process control probe which monitors certain process characteristics within an ultrasound process tank. The probe includes an enclosure, e.g., made from polypropylene, that transmits ultrasound energy therethrough. The enclosure houses a liquid that is responsive to the ultrasound energy in some manner such as to create free radicals and ions from which conductivity can be measured. This conductivity provides an indication as to the number of cavitation implosions per unit volume being imparted to the process chemistry within the tank. A conduit from the enclosure to a location external to the process chemistry is used to measure the characteristics of the liquid in response to the energy. In other aspects, a thermocouple is included within the enclosure and/or on an external surface of the enclosure (i.e., in contact with the process chemistry) so as to monitor temperature changes within the enclosure and/or within the process chemistry. Other characteristics within the tank and/or enclosure can be monitored over time so as to create time-varying functions that provide other useful information about the characteristics of the processes within the tank.
In one aspect, the invention provides an ultrasound system for moving contaminants upwards within a processing tank, which holds process liquid. An ultrasound generator produces ultrasound drive signals through a range of frequencies as defined by an upper frequency and a lower frequency. A transducer connected to the tank and the generator responds to the drive signals to impart ultrasound energy to the liquid. A controller subsystem controls the generator such that the drive signals monotonically change from the upper frequency to the lower frequency to drive contaminants upwards through the liquid.
In one aspect, the controller subsystem cyclically produces the drive signals such that the generator sweeps the drive signals from the upper frequency to the lower frequency over a first half cycle, and from the lower frequency to the higher frequency over a second one half cycle. The subsystem of this aspect inhibits the drive signals over the second half cycle to provide a quiet period to the liquid.
In other aspects, the first and second one-half cycles can have different time periods. Each successive one-half cycle can have a different time period such that a repetition rate of the first and second half cycles is non-constant. Or, the first one-half cycle can have a fixed period and the second one-half cycle can be non-constant.
In one aspect, the first half cycle corresponds to a first time period and the second one half cycle corresponds to a second time period, and the subsystem varies the first or second time periods between adjacent cycles.
Preferably, the subsystem includes means for shutting the generator off during the second one half cycle.
In another aspect, the subsystem includes an AM modulator for amplitude modulating the drive signals at an AM frequency. In one aspect, the AM modulator sweeps the AM frequency. In another aspect, the AM modulator sweeps the AM frequency from a high frequency to a low frequency and without sweeping the AM frequency from the low frequency to the high frequency. The subsystem can further inject a quiet or degas period before each monotonic AM frequency sweep.
In another aspect, there is provided an ultrasound system for moving contaminants upwards within a processing tank, including: a processing tank for holding process liquid, an ultrasound generator for generating ultrasound drive signals through a range of frequencies defined between an upper frequency and a lower frequency, at least one transducer connected to the tank and the generator, the transducer being responsive to the drive signals to impart ultrasound energy to the liquid, and a controller subsystem for controlling the generator through one or more cycles, each cycle including monotonically sweeping the drive signals from the upper frequency to the lower frequency, during a sweep period, and recycling the generator from the lower frequency to the upper frequency, during a recovery period, the sweep period being at least nine times longer than the recovery period.
In one aspect, the controller subsystem varies a time period for each cycle wherein the time period is non-constant.
In still another aspect, an ultrasound system is provided for moving contaminants upwards within a processing tank, including: a processing tank for holding process liquid; an ultrasound generator for generating ultrasound drive signals; at least one transducer connected to the tank and the generator, the transducer being responsive to the drive signals to impart ultrasound energy to the liquid; and an amplitude modulation subsystem for amplitude modulating the drive signals through a range of AM frequencies characterized by an upper frequency and a lower frequency, the subsystem monotonically changing the AM frequency from the upper frequency to the lower frequency to drive contaminants upwards through the liquid.
In one aspect, the generator sweeps the drive signals from upper to lower frequencies to provide additional upwards motion of contaminants within the liquid.
In another aspect, the AM frequencies are between about 1.2 khz and a lower frequency of 1 Hz. The AM frequencies can also cover a different range, such as between about 800 Hz and a lower frequency of 200 Hz.
In another aspect, the invention provides a multi-generator system for producing ultrasound at selected different frequencies within a processing tank of the type including one or more transducers. A generator section has a first generator circuit for producing first ultrasound drive signals over a first range of frequencies and a second generator circuit for producing second ultrasound drive signals over a second range of frequencies. The generator section has an output unit connecting the drive signals to the transducers. Each generator circuit has a first relay initiated by a user-selected command wherein either the first or the second drive signals are connected to the output unit selectively.
In one aspect, a 24VDC supply provides power for relay coils.
In another aspect, each generator circuit has a second relay for energizing the circuit. Two time delay circuits can also be included for delay purposes: the first time delay circuit delaying generator circuit operation over a first delay period from when the second relay is energized, the second time delay circuit delaying discontinuance of the first relay over a second delay period after the generator circuit is commanded to stop. The first delay period is preferably longer than the second delay period such that no two generators circuits operate simultaneously and such that all generator circuits are inactive during switching of the first relay.
Each relay can include a 24 VDC coil. A selecting device, e.g., a PLC, computer, or selector switch, can be used to select the operating generator circuit. At selection, 24 VDC connects to the two relays of this operating generator circuit. Preferably, each relay coil operates at a common voltage level.
In one aspect, a variable voltage ultrasound generator system is provided, including: an ultrasound generator; a switching regulator for regulating a 300 VDC signal to +12V and +15V lines, the generator being connected to the +12V and +15V lines; and a power factor correction circuit connected to AC power. The power factor correction circuit provides 300 VDC output to the generator and to the regulator. The generator thus being automatically operable from world voltage sources between 86 VAC and 264 VAC.
In another aspect, a variable voltage ultrasound generator system is provided, including: an ultrasound generator; and a universal switching regulator (known to those skilled in the art), connected to AC power, for regulating a set of DC voltages to the generator. The generator thus being automatically operable from world voltage sources between 86 VAC and 264 VAC.
In another aspect, a double compression transducer is provided for producing ultrasound within an ultrasound tank. The transducer has a front plate and a backplate. At least one piezoceramic is sandwiched between the front plate and backplate. A bias bolt with an elongated bias bolt body between a bias bolt head and a threaded portion extends through the front plate and the piezoceramic and is connected with the backplate (either by screwing into the backplate or by a nut screwed onto the bias bolt adjacent the backplate). The bias bolt also forms a through-hole interior that axially extends between the head and the threaded portion. A second bolt with an elongated body between a second bolt head and a threaded tip is disposed within the bias bolt. The second bolt head is rigidly attached to the tank and a nut is screwed onto the threaded tip and adjacent to the backplate. The bias bolt thus provides a first level of compression of the piezoceramic. The second bolt provides a second level of compression of the front plate and the tank, particularly when epoxy is used to bond between the front plate and the tank.
In still another aspect, a variable voltage ultrasound generator system is provided. The system includes an ultrasound generator and a constant peak amplitude triac circuit connected to AC power. The triac circuit converts the AC power to a 121.6 voltage peak, or less, AC signal. A bridge rectifier and filter connects to the AC signal to rectify and filter the AC signal and to generate a DC voltage less than (86)({square root over (2)}) volts. A switching regulator regulates the DC voltage to 12 VDC and 15 VDC; and the generator connects to the DC voltage, the 12 VDC and the 15 VDC. In this manner, the generator is thus automatically operable from world voltage sources between 86 VAC and 264 VAC.
The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.
In another aspect, the multiple frequency invention described herein is a new class of liquid cleaning and processing equipment where there is one transducer array and one generator that produces a series string of different frequencies within two or more non-overlapping continuous frequency ranges. The transducer array is capable of responding to electrical frequency signals to produce intense sound energy at any frequency within two or more distinct frequency bands. The generator is capable of supplying an electrical frequency signal at any frequency within continuous frequency ranges contained within two or more of the transducer array""s frequency bands.
The generator and transducer array produce a series string of different frequency sound waves. The first produced frequency is typically followed by a different second frequency that is in the same frequency range as the first frequency, then this second frequency is typically followed by a different third frequency that is in the same frequency range as the first two frequencies, and this pattern continues for at least the lifetime of a sound wave in the liquid (typically 20 to 70 milliseconds). This results in multiple closely related frequencies of the same frequency range adding up within the liquid to a value of high intensity sound. This high intensity multiple frequency sound field is typically maintained long enough to accomplish a specific part of the cleaning or processing cycle, then the electrical frequency signal output of the generator is controlled to jump to a frequency in a different frequency range, typically in a different frequency band, where different frequencies are again strung together for at least the lifetime of a sound wave in the liquid.
This invention is an improvement over prior art multiple frequency systems because by stringing together different frequencies from the same frequency range for at least the lifetime of a sound wave in the liquid, the sound intensity of these closely related frequencies builds up to a higher value than with any of the prior art multiple frequency systems. This higher intensity sound field does the improved cleaning or processing within the frequency range and then the system jumps to another frequency range where the cleaning or processing effect is different. Again, in the second frequency range the sound intensity builds up to a higher value than with any prior art multiple frequency system and, therefore, the improvement in cleaning or processing occurs within this second frequency range. Also, by maintaining the production of sound in each frequency range for a minimum of 20 milliseconds, there is substantially no intense sound energy produced at frequencies outside of the frequency ranges, this further adds to the build up of the intensity of the sound energy. Each of these improved effects in each of the different frequency ranges adds up to a process that is superior to prior art methods.
A variation of the invention substitutes a fraction of a cycle of a frequency strung together with other fractions of a cycle of sound at different frequencies within a given frequency range before jumping to a different frequency range. Another variation inserts a degas time between jumps from one frequency range to another. Another variation controls the generator to cycle through the frequency ranges in different orders, i.e., several permutations of the frequency ranges are introduced into the liquid during the cleaning or processing cycle. Another variation defines each permutation of a frequency range to be a cleaning packet and the order in which these cleaning packets are delivered to the liquid is varied to produce different cleaning effects. Still other variations introduce phase lock loops, duty cycle control, amplitude control, PLC control, computer control, quiet times, active power control, series resistor VCO control, DAC VCO control, cavitation probe feedback to the generator and digital code frequency selection. In general, this invention is useful in the frequency spectrum 9 kHz to 5 MHz.
The foregoing and other objects of are achieved by the invention, which in one aspect comprises a system for coupling sound energy to a liquid, including at least two transducers forming a transducer array adapted for coupling to a liquid in a container. The transducer array is constructed and arranged so as to be capable of producing intense sound energy in the liquid at any frequency within at least two non-overlapping frequency bands. The system further includes a signal generator adapted for producing a driver signal for driving the transducer array at any frequency from one or more continuous frequency ranges within at least two of the frequency bands. The signal generator drives the transducer array to produce the intense sound energy characterized by a series string of different frequencies within one of the continuous frequency ranges. The generator further drives the transducer array to discontinuously jump amongst the frequency ranges, so as to generate intense sound energy characterized by a series string of different frequencies within at least one additional frequency range in at least one additional frequency band.
Another embodiment of the invention further includes a controller for controlling the frequency of the ultrasound energy within the series string of different frequencies. The controller also controls a duration of each frequency in the series string.
In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a staircase function.
In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a series of monotonically decreasing frequencies.
In another embodiment of the invention, the series of monotonically decreasing frequencies occurs for at least ninety percent of an interval during which the transducer array couples intense sound energy to the liquid.
In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a series of frequencies defined by a predetermined function of time.
In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a series of frequencies swept from a first frequency to a second frequency at a constant sweep rate.
In another embodiment of the invention, the series of frequencies is swept at a non-constant sweep rate.
In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by a random or chaotic series of frequencies.
In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by at least a first group of frequencies from a first frequency band, and a second group of frequencies from a second frequency band, such that at least two groups of frequencies adjacent in time are from different frequency bands.
In another embodiment of the invention, the series string of different frequencies further includes at least one degas interval between periods of time having ultrasound energy.
In another embodiment of the invention, the intense sound energy in the series string of different frequencies is characterized by at least a first group of frequencies from a first frequency band, and a second group of frequencies also from the first frequency band, such that at least two groups of frequencies adjacent in time are from the same frequency band.
In another embodiment of the invention, the intense sound energy in each of the series string of different frequencies is characterized by at least a fraction of a cycle of the distinct frequency.
In another embodiment of the invention, the fraction of a cycle is one-half of a cycle, and each successive one-half cycle represents a different frequency.
In another embodiment of the invention, the intense sound energy includes frequencies selected from the frequency spectrum 9 kHz to 5 MHz.
In another embodiment of the invention, the frequency ranges are characterized by a center frequency. The center frequency of each higher frequency range is a non-integer multiple of the center frequency of the lowest frequency range, so as to prevent one or more Fourier frequencies of a periodic wave from forming in the liquid.
In another embodiment of the invention, the controller includes a PLC or a computer.
Another embodiment of the invention further includes a probe adapted for measuring one or more parameters associated with the liquid corresponding to sound-produced effects in the liquid. The controller alters the generator driver signal as both a predetermined function of the measured parameters, and according to the desired purpose of the system.
In another embodiment of the invention, each specific frequency range is represented by a distinct digital code. The controller initiates a transition from a first frequency range to a second frequency range in response to the digital code transitioning from a digital code representative of the first frequency range to the digital code representative of the second frequency range.
In another embodiment of the invention, the center frequency of each frequency range corresponds to an output of a voltage controlled oscillator. The output of the voltage controlled oscillator corresponds to an input control signal, and the input control signal is determined by a series string of resistors. The total string of resistors produces the lowest frequency range and each higher string of resistors produces each higher frequency range.
In another embodiment of the invention, the intense sound energy includes ultrasound energy.
In another embodiment of the invention, the intense sound energy in the series string of different frequencies occurs continuously for at least 20 milliseconds, within each of the continuous frequency ranges.
In another embodiment of the invention, the output power level of the driver signal is actively maintained by comparing an actual output power level to a specified output power level, and adjusting parameters of the driver signal to make the actual output power level substantially equal to the specified output power level. The parameters of the driver signal may be either amplitude, duty cycle, or some combination thereof.
In another embodiment of the invention, the intense sound energy characterized by the series string of different frequencies further includes one or more quiet time intervals characterized by a substantial absence of intense sound energy.
In another embodiment of the invention, the quiet time intervals are distributed periodically among the intervals of intense sound energy. In yet another embodiment, the quiet time intervals are distributed randomly or chaotically among the intervals of intense sound energy.
In another embodiment of the invention, the quiet time intervals are distributed among the intervals of intense sound energy according to a predetermined function of time.
In another embodiment of the invention, the center frequency for each frequency range is optimized by an automatic adjustment from a circuit that maintains a substantially zero phase shift between an associated output voltage and output current at the center frequency.
In another embodiment of the invention, the order of frequency range transitions varies such that several permutations of frequency ranges can be introduced into the liquid. In other embodiments, each permutation of frequency ranges is defined as a specific cleaning packet, and the order in which the cleaning packets are introduced into the liquid is changed such that each different order produces a different cleaning effect.
In another embodiment of the invention, substantially no intense sound energy is produced at frequencies outside of the frequency ranges.
In another embodiment of the invention, the container holding the liquid is constructed from materials resistant to detrimental effects of the liquids. These materials may include tantalum, polyetheretherketone, titanium, polypropylene, Teflon, Teflon coated stainless steel, or combinations thereof, or other similar materials known to those in the art.
In another embodiment of the invention, the signal generator is capable of producing an infinite number of frequencies contained within each of the unconnected continuous frequency ranges.
In another embodiment of the invention, the signal generator produces an output signal including the FM information for synchronizing other generators or power modules.
In another embodiment of the invention, the center frequency of each frequency range corresponds to an output of a voltage controlled oscillator. The output of the voltage controlled oscillator corresponds to an input control signal, and the input control signal is generated by a DAC (digital-to-analog converter). In other embodiments, the digital input to the DAC produces a stepped staircase analog output from the DAC, resulting in a stepped, staircase sweeping function within a frequency range. In yet another embodiment, the digital input to the DAC produces a random or chaotic staircase analog output from the DAC, resulting in a random or chaotic staircase sweeping function within a frequency range.
In another aspect, the invention comprises a system for coupling sound energy to a liquid. The system includes at least two transducers forming a transducer array adapted for coupling to a liquid in a tank, and the transducer array is constructed and arranged so as to be capable of producing intense sound energy in the liquid at any frequency within at least two non-overlapping frequency bands. The system further includes a signal generator adapted for producing a driver signal for driving the transducer array at any frequency from one or more continuous frequency ranges within at least two of the frequency bands. The signal generator drives the transducer array so as to produce intense sound energy characterized by a plurality of changing frequencies within a first frequency range, followed by a plurality of changing frequencies within a second frequency range. The system so operating reduces a strong antinode below the liquid-to-air interface.
In another aspect, the invention comprises a system for coupling sound energy to a liquid, that includes at least two transducers forming a transducer array adapted for coupling to a liquid in a tank. The transducer array is constructed and arranged so as to be capable of producing intense sound energy in the liquid at any frequency within at least two distinct frequency bands. The system further includes a signal generator adapted for producing a driver signal for driving the transducer array at any frequency from one or more continuous frequency ranges within the at least two frequency bands. The center frequencies of the higher frequency ranges are non-integer multiples of the center frequency of the lowest frequency range to prevent two or more Fourier frequencies of a periodic wave from forming in the liquid. The signal generator drives the transducer array to produce sound energy corresponding to a first set of frequencies from a first frequency range, then produces sound energy corresponding to a second set of frequencies from a second frequency range. The transition from the first frequency range to the second frequency range is discontinuous and occurs after a time interval at least as long as the lifetime of sound energy in the container for frequencies from the first frequency range. The sound energy corresponding to the second set of frequencies continues for a time interval at least as long as the lifetime of sound energy in the container for frequencies from the second frequency range.
In another aspect, the invention comprises multiple frequency generator capable of producing an output signal characterized by any frequency within two or more non-contiguous, continuous frequency ranges. The generator is controlled to change the frequency within a frequency range, and then to change frequencies from one frequency range to a second frequency range before beginning the changing of frequencies in this second frequency range.
In another aspect, the invention comprises a method of delivering multiple frequencies of intense sound waves to a liquid. The method includes the step of coupling to the liquid an array of transducers that are capable of producing sound energy in the liquid at an infinite number of different frequencies contained within two or more non-contiguous, continuous frequency bands. The method also includes the step of driving the transducer array with a generator capable of producing substantially all of the frequencies within continuous frequency ranges contained within two or more of the transducer array frequency bands. The method further includes the step of controlling the generator so that the produced frequencies change within the frequency ranges according to a function of time, and the frequencies jump amongst the frequency ranges.
In another aspect, the present invention is directed to the creation of an AC switch by electronic circuitry or electromechanical devices, such as relays. The AC switch as presented in this invention will exchange a modifying circuitry (which contains resistive, reactive, and active components) into and out of the power section of an ultrasound generator. Therefore, the output of the ultrasound generator will be modified by the modification circuitry disclosed, by way of example, herein. The AC switch is operatively connected to the modification circuitry. It switches the modification circuitry into and out of the output stage of the generator. The control circuitry is associated with the AC switch and is adapted to turn off and turn on the AC switch. The AC switch will swap resistive, reactive and active components and networks of these components into and out of the power section of ultrasound frequency generators. The present invention provides a simple and reliable manner to increase the number of parameters and diversify the capabilities of an ultrasound generator.
The AC switch introduces a modification circuit that is able to (1) maintain full power output from a multiple frequency ultrasound generator as the center frequency of the generator is changed, (2) step sweep the output of an ultrasound oscillator, and (3) vary the output power and amplitude of a non self-oscillating ultrasound generator. A fixed frequency oscillator can be modified to accomplish certain of these functions and to sweep frequency. This is accomplished by the step sweeping and successive AC switching in of capacitors and/or inductors (i.e. modification circuitry).
This patent will suggest a number of applications in which the AC switch is created by triacs. A triac is a three terminal semiconductor, which controls current in either direction. The triac is suited to create a simple and less expensive AC switch than the use of transistors. Nevertheless, it will be obvious to those skilled in the art that other circuitry can be substituted for triacs. One example of such other circuitry, which simulates a triac, is one that includes back to back silicon-controlled rectifiers. Also, a series/parallel active device configuration or bi-directional lateral insulated gate bipolar transistor, can act as the AC switch.
The phrase xe2x80x9cmodification circuitryxe2x80x9d as used herein is defined as resistive, reactive and active components and networks of these components. The circuitry will have two main leads and one or more control leads available for active components or networks containing active components. One of ordinary skill in the art will readily appreciate that it is possible to introduce a different value of a resistive or reactive component through the use of a transformer; therefore, in some cases a transformer winding or tap can be the part of the modification circuitry that is switched by the AC switch.
The modification circuitry is placed in parallel with an AC switch when it is required that the modification circuitry be inserted into a conduction line of the ultrasound generator. The modification circuitry is placed in series with an AC switch when it is required that the modification circuitry be inserted between two nodes of the ultrasound generator. When connected in series, the modification circuitry is inserted at any time in the cycle by turning on the AC switch. In the case of a parallel connection, the modification circuitry is removed from the generator when the AC switch is on. The reverse effect will happen when the AC switch is turned off. The addition of a control circuitry to the AC switch supplies turn on and off signals to the AC switch. Where the AC switch is a triac, the control circuitry will provide (1) a turn off signal to the ultrasound generator for a period of time at least as long as the triac turn off time, (2) the turn off signal to the triac for a period of time at least as long as the triac turn off time, and (3) concurrent signals for a period of time at least as long as the triac turn off time. The use of this control circuitry is necessary due to the fact that the speed of triacs is too slow to allow them to go off when conducting an ultrasound current.
Another embodiment of the invention includes modification circuitry capable of modifying the following parameters of the output of an ultrasound generator: frequency; amplitude; power; impedance; and waveform. The parameter will change in accordance to the purpose of the application or generator. The modification includes at least one capacitor, one inductor, or one resistor. Finally, it can also include an active/passive network with a control circuitry adapted to control the active components in the network.
In another embodiment of the invention, a control circuitry capable of supplying a turn off signal to the AC switch for a duration D1 is illustrated. If the AC switch is a triac, the control circuitry will also supply a turn off signal D2 to the generator, where D1 and D2 are concurrent for a time equal to or greater than the triac turn off time. The same will apply if the AC switch is comprised of back to back silicon controlled rectifiers. In the case of the modification of the output frequency of an ultrasound oscillator, the xe2x80x9ccontrollerxe2x80x9d will represent the control circuit. This controller can be further modified to selectively activate or deactivate components so as to step sweep the output frequency of an oscillator.
Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising two or more transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands, and one or more ultrasound generators adapted for producing driver signals for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein at least one frequency range is within the microsonic range of frequencies; and, wherein the driver signals in the microsonic range of frequencies are synchronized with a common FM signal; and, wherein the driver signals of the one or more ultrasound generators drive the transducers to produce ultrasound in the liquid characterized by a frequency that sweeps at random, chaotic or pseudo random sweep rates within at least one of the frequency ranges in one of the at least two frequency bands; and, wherein the sweep is monotonic from high frequency to low frequency with a recovery time from low frequency to high frequency that is a shorter time than the monotonic sweep; and, wherein the driver signals are amplitude modulated at a modulation frequency that changes randomly, chaotically or pseudo randomly; and, wherein the one or more ultrasound generators each have an output stage, which comprises, a) modification circuitry which modifies the output stage; b) an AC switch, operatively connected to the modification circuitry, which switches the modification circuitry into and out of the output stage of the ultrasound generator; and c) control circuitry, associated with the AC switch and with the one or more ultrasound generators, which is adapted to turn off and turn on the AC switch, wherein the control circuitry, AC switch and modification circuitry changes the one or more ultrasound generator driver signals to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by a frequency that sweeps at random, pseudo random or chaotic sweep rates within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands. In yet another embodiment of the invention, this system adds power control to the ultrasound by an amplitude modulated driver signal that has off times that vary randomly, chaotically or pseudo randomly while maintaining a specified duty cycle for power control.
Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising one or more transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands, and an ultrasound generator adapted for producing a driver signal for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein the driver signal of the ultrasound generator drives the transducers to produce ultrasound in the liquid characterized by successive frequencies within at least one of the frequency ranges in one of the at least two frequency bands; and, wherein the ultrasound generator has an output stage, which comprises, a) modification circuitry which modifies the output stage; b) an AC switch, operatively connected to the modification circuitry, which switches the modification circuitry into and out of the output stage of the ultrasound generator; and c) control circuitry, associated with the AC switch and with the ultrasound generator, which is adapted to turn off and turn on the AC switch, wherein the control circuitry, AC switch and modification circuitry changes the ultrasound generator driver signal to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by successive frequencies within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands.
Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising, two or more transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands, and, one or more ultrasound generators adapted for producing driver signals for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein at least one frequency range is within the microsonic range of frequencies; and, wherein the driver signals of the one or more ultrasound generators drive the transducers to produce ultrasound in the liquid characterized by a frequency that sweeps at random, chaotic or pseudo random sweep rates within at least one of the frequency ranges in one of the at least two frequency bands; and, wherein the driver signals are amplitude modulated at a modulation frequency that changes randomly, chaotically or pseudo randomly; and, wherein the one or more ultrasound generators each have an output stage, which comprises, a) modification circuitry which modifies the output stage; b) an AC switch, operatively connected to the modification circuitry, which switches the modification circuitry into and out of the output stage of the ultrasound generator; and c) control circuitry, associated with the AC switch and with the one or more ultrasound generators, which is adapted to turn off and turn on the AC switch, wherein the control circuitry, AC switch and modification circuitry changes the one or more ultrasound generator driver signals to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by a frequency that sweeps at random, pseudo random or chaotic sweep rates within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands.
Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising at least two transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands; an ultrasound generator adapted for producing a driver signal for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein at least one of the frequency ranges is in the microsonic range of frequencies; and, wherein the driver signal of the ultrasound generator drives the transducers to produce ultrasound in the liquid characterized by successive frequencies within at least one of the frequency ranges in one of the at least two frequency bands; the ultrasound generator changes the driver signal to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by successive frequencies within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands.
Another embodiment of the invention is a system for coupling ultrasound to a liquid, comprising two or more transducers adapted for coupling to a liquid, the transducers constructed and arranged so as to be capable of producing ultrasound in the liquid at frequencies within at least two frequency bands, and, one or more ultrasound generators adapted for producing driver signals for driving the transducers at frequencies in one or more frequency ranges within each of the at least two frequency bands; wherein the driver signals of the one or more ultrasound generators drive the transducers to produce ultrasound in the liquid characterized by a frequency that sweeps at random, chaotic or pseudo random sweep rates within at least one of the frequency ranges in one of the at least two frequency bands; and, wherein the driver signals are continuous wave; and, wherein the one or more ultrasound generators each have an output stage, which comprises a) modification circuitry which modifies the output stage; b) an AC switch, operatively connected to the modification circuitry, which switches the modification circuitry into and out of the output stage of the ultrasound generator; and c) control circuitry, associated with the AC switch and with the one or more ultrasound generators, which is adapted to turn off and turn on the AC switch, wherein the control circuitry, AC switch and modification circuitry changes the one or more ultrasound generator driver signals to further drive the transducers to change frequency to a different frequency range in a different frequency band, so as to generate ultrasound characterized by a frequency that sweeps at random, pseudo random or chaotic sweep rates within at least one additional frequency range in at least one additional frequency band of the at least two frequency bands.
Another embodiment of the invention is an ultrasound generator having an output signal that is frequency modulated with a sweeping frequency waveform and amplitude modulated with a changing frequency; wherein the sweep rate of the sweeping frequency waveform changes randomly, chaotically or pseudo randomly; and, wherein the amplitude modulation frequency changes randomly, chaotically or pseudo randomly.
Another embodiment of the invention is an ultrasound generator having an output signal that is frequency modulated with a sweeping frequency waveform and has continuous wave for its amplitude modulation; wherein the sweep rate of the sweeping frequency waveform changes randomly, chaotically or pseudo randomly.
The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.